Help with diagnosis

I have a 82 xj650 maxim that I recently pulled the carbs to do a partial rebuild to fix sluggish acceleration. Everything went great floats were wet set to spec, everything was cleaned and bench synced.

While vacuum syncing the carbs i started to run into an issue. The bike would hang when I revved the motor and it would sometimes slowly drop.

Today...I inserted a yics eliminator tool to try and re calibrate and i got the idle and carb to a good place. The main problem I am having now is when i took it for a test run the bike would spike a high rev when stopping. I debated a vacuum leak and notice a boot between the air box and carb not sitting right. I still need to colortune the carbs, I am just not sure if the issue i am having is a vacuum or fuel mixture issue.

any help is appreciated! this is my first bike so its hard for me to trouble shoot.

 

Vac sync needs to be done with the bike warm. Take it for a good 10+ min ride, then put a fan toward the engine and do the sync. Adjust your idle so it stays around 1200, then do the sync and adjust idle as necessary. Remember to oil the seals on the eliminator to avoid them melting in your YICS port.

Definitely fix that boot. I always just use a small flathead screwdriver for that.

Colortuning comes last. After all other quirks are figured out.

 

Here is an image showing how ther boots are fitting, you can see some of them aren't sitting right.

When i did the cab sync the bike was warmed up, i'll see if i can post a video tomorrow of the carbs sync level.

Would these issues cause the bike to rev high when I come to a stop?

 

Yes

 

Mine was doing that after my tune. Turned out that my throttle cable was sticking and not letting the butterfly valves to snap shut.

 

on those boots, Take a look at the area under the clamp, you should find a oval mark in the rubber. That goes on top. Some times the clamp gets in the way, I only clamp 1&4 , 2&3 get no clamp or a long zip tie.

 

The airbox-to-carb boots are not the cause of a hanging idle,
the integrity of the intake boots, gaskets, rubber caps, petcock hose, and throttle-shaft seals are in question.

Check for vacuum leak.

Test with an unlit propane torch, can of ether/starting fluid,
or if you're bold, flow a garden hose over your suspected leaky item.

 

But it CAN be a source.... Have had it happen. I've also had it be the source of the oroblem for another bike that wouldn't start.....

 

When it's revving high, gently press down on the sync screw (gently) and see if the idle drops. This will let you know if either butterfly is binding, which only really presents the symptom when it's warm. each butterfly needs to *tink* when each of their actions are released, if you follow me.

I've had a similar problem, which is something to not overlook either. if that proves to be the issue you'll likely need to split the rack and reset each butterfly.

 

I got the carbs synced up nice and level and while i was doing it the bike would start to rev high to 3k rpm. to lower it i would adjust the idle screw and it would come back down to 1500 rpm. i havent rode the bike yet to test it but i suspect it will still spike revs.

I was using a DYI auxiliary tank so i am not sure it is the petcock since it would still spike the revs. The one symptom i did have prior and part of why i pulled the carbs off is that i was getting fuel into my oil. so it might possibly be the petcock.

how do you test the throttle shaft seals?

 

Fuel in the oil is a float/float level issue. The petcock supplies fuel; the floats are responsible for shutting off fuel at the right level. Gas in the oil is NOT a "petcock issue" it indicates a float problem of some sort.

 

Ok cool, then that should have been fixed when i reset the float and swapped out the needles for the all metal ones(not in that order). i read somewhere that gas leaking into the oil could be from a leaky petcock. Glad to know now that isn't the issue. Saved me from buying a new petcock.

 

I didn't say it isn't an issue. It isn't the CAUSE of the issue; it can enable a poorly sealing float valve to not do its job.

If your floats are working correctly a leaky petcock can't contribute to the gas in the oil issue. If the floats are working correctly you could (in theory) leave it on PRI and nothing bad would happen.

 

Revs can hang on a little if the pilots are out of adjustment.
You asked about checking the V-seals. Use a torch and the revs will spike if they are leaking vacuum.

 

I did the propane trick and it didnt increase the revs. so i am happy about that. However when i started the bike today there was a popping sound coming out of the motor as if the gas wasnt igniting properly. some sort of back pressure/blowback. this is making me think the fuel mixture screws are open too wide.

I made this video of the motor running and the bike idling high. Hearing the way the motor runs in the video I am starting to get concerned there might be an issue with the motor. One of the odd things about the high rev is that it will do it out of no where and i am not sure at this point what else to look for.

I didn't have this problem before i pulled the carbs.

[video=400,180]http://player.vimeo.com/video/105828728[/video]

 

So i am still having the issues and i am about to pull the carbs again. Today i noticed the shaft connection that the fuel line connects to spins like it is loose. is that supposed to move? it rotates up and down and would that cause the issue?

 

I Feel your Pain.

I'm having trouble with Carbs on my 1980 Seca
With the Bike Running i Pulled the Vacuum Blanking Plugs off one at a time
There was no change on 2 Cylinders, No2 and No4, Obviously an Air Leak,

I found that there was an Air Leak in the Butterfly Shafts,
What i did was, Wearing a rubber work glove, Marigold gloves will do
I Pressed my finger over the Shaft of No4 Cylinder
And the Revs Started to Rise,
You Could give it a Go, See If It Works for You.

Hope this Helps

 

Been busy with work but this weekend i got a lot done. I put on a new MC... what a difference. Now the front tire actually stops tight! new clutch cable, throttle cable and pulled the carbs to check the valve and redo the bench sync. Everything looks spot on. I decided to check the airbox and i noticed a screw was missed on the left side. Once i put a new screw on and pushed the box forward it is now allowing the boots to sit flush. Not sure how that screw vanished but its fixed now. previous owner i guess...

Tomorrow i plan on re-vacuum syncing the carbs and color tune them. Originally i have 2.5 turns on the mixture screws i lowered it down to one full turn just to see if that helps.
When i pulled the bowls off today to see if the jets were ok the sizes are as follows 112 and 42. Looks like the previous owner made them larger. I wonder if he added a jet kit.

 

I will definitely try this tomorrow. Just to make sure you put your finger over the C clips and the revs rose up?

 

Your valve clearances are in spec, correct? If not, then trying to vacuum sync is a waste of time.